Research on the possibilities of partially replacing skim milk powder in yogurt manufacture

The aim of this study was to determine the changes of physical, chemical and sensory properties of partially replacing skim milk powder with whey powder in yogurt manufacture during storage period. For this purpose, experimental yogurts were manufactured with raw milk, which supplemented with whey powder at different levels (whey powdcr/skim milk powder; 0/3.0, 0.5/2.5, 1.0/2.0, 1.5/1.5, 2.0/1.0, 2.5/0.5 and 3.0/0 %). Total solid, fat, non-fat solid, protein and ash contents of yogurt samples were analyzed in the first day of storage. Viscosity, syneresis, titratable acidity, pH, lactic acid, volatile free fatty acids, acetaldehyde, tyrosine values, and sensory assessment were examined on days of 1, 7 and 14 of the storage. According to results obtained; effect of whey powder rates on the viscosity value, syneresis rate, free fatty acids and tyrosine content of yogurt samples were found to be significant (p<0.01), while, titratable acidity, pH value, lactic acid and acetaldehyde contents were found to be insignificant. It was observed that the viscosity value, titratable acidity, lactic acid, volatile free fatty acids and tyrosine contents of yogurt samples increased (p<0.01) whereas pH value, syneresis rate and acetaldehyde content decreased (p<0.01) during storage period. In the organoleptic properties of samples, the lowest mean total score was 17.38 for G (3.0%) sample whereas the highest mean total score was 22.64 for C (1.0%) sample based on 25 point. Addition of whey powder until at the level of 1.0% was not caused adverse effect on the sensory evaluations of panelists. Moreover, C sample was preferred more than A (control) sample by panelists. Yogurt samples contained whey powder up to 2% level had 20 total score specified by TS-1330 Yogurt Standard and it was concluded that whey powder may be used in the yogurt manufacture until this level. 2002, 58 pages Keywords: Yogurt, whey powder, skim milk powder, analysis, storage period.